This invention relates to a tire building apparatus and a method for pulling and holding a tubular element of a tire component on the circumference of a tire building drum in a green tire production step.
It has been a common procedure in tire building processes in which a tubular tread ring is formed by winding a rubber made belt element and a tread element around a tire building drum, subsequently the tread ring is removed from the tire building drum by a tread ring transferring apparatus and transferred to a tubular carcass-ply which is formed independently and the tread ring is placed around the outer circumference of the carcass-ply to unite them together to form a one piece unit called a green tire.
One example of the tread ring building drum for building the tread ring is shown in FIG. 8. The tread ring building drum is divided into several pieces along the circumferential direction thereof and consists of a plurality of segments 2 that are movable in the radial direction. FIG. 8 shows an expanded state of the segments 2 (an expansion state of the tread ring building drum) 1 and the segments 2 are moved to retracted states, i.e., moving towards a radially inward direction of the tread ring building apparatus, for enabling the removal of the tread ring out of the tread ring building drum 1 with ease.
Each of the segments 2 is provided with an opening 3 which communicates with a negative (vacuum) pressure supply source (suction power source; not shown) and the tread ring material 4 (as one of the tire components) is pulled towards the segments by the suction force generated through the openings 3 to properly maintain the holding state of the tread ring material 4 to the tread ring building drum 1.
In the aforementioned tire building apparatus, the openings 3 are arranged along the circumferential direction of the tread ring building drum 1 at equal pitch P. This equal pitch arrangement of the openings 3 along the circumference of the drum 1 causes some problems regarding the driver's feel of comfort while driving on a tires produced from the apparatus. More specifically, as a result of the equal pitch arrangement of the suction openings 3, it is highly likely that the tread ring form a plurality of strained portions (in the form of indents) 5 along the outer circumference of the tread ring at equal pitch as shown in FIG. 8. It has been known to the person skilled in this art that a tire with strained portions 5 a regular pitch along the outer circumference thereof increases a "RFV (radial force variation)" at its particular variation mode, resulting in degrading the vibration characteristics of the tire as a final product. It in turn adversely affects driving comfort or even produces some abnormal noise. Thus, the formation of strained portions 5 at equal pitch along the outer circumference of the tread ring, due to the equal pitch arrangement of the suction openings 3, adversely affects vibration characteristics of the tire, resulting in driving comfort of the driver being degraded.
Accordingly, there is a need to avoid degradation of the vibration characteristics of the tire without sacrificing the ability of pulling and holding the tread ring material 4 to the tread ring building drum 1.